1. Field of the Invention
This invention relates to modified, acrylate polymer compositions featuring reduced brittleness, such polymers being particularly suitable as dental/medical cements and restorative materials and for manufacturing dental prosthetics.
2. Description of the Related Art
Polymeric materials based on the esters of methacrylic acid have found widespread industrial and medical applications. Their role is particularly prominent in dentistry where they have become a base for modern restorative materials, cements, varnishes, cavity liners and sealers. In medicine perhaps the most important uses of acrylic resins include contact lenses and cements used for hip restorations.
Many of these applications require the material to meet a combination of requirements with respect to their chemical, optical and mechanical properties and, frequently, biological compatibility. While acrylic resins, due to a variety of available monomers, usually make it possible to compound a blend which, upon cure, will result in a polymer meeting the requirements of tissue biocompatibility, wear resistance, translucency, mechanical strength or hardness, they frequently fail or are less than satisfactory in applications requiring flexibility. It is especially true in situations where thin layers of polymers are exposed to flexural forces; for example, while placing or removing a well-fitted device. Another example of situations where the greater flexibility and impact resistance of acrylic polymers would be highly desirable are applications where the devices made of such polymeric materials are exposed to rapid or repetitiously applied forces. Especially vulnerable are thin areas of such objects.
In applications requiring longevity, mechanical strength and resistance to exposure to environments which may have a deteriorating effect on the polymeric material by means of wear, chemical reaction, exposure to heat, light, etc., cross-linked acrylic polymers are generally preferred over the linear ones. Consequently, in addition to monounsaturated monomers frequently used in such applications, exemplified by alkylmethacrylates, tetrahydrofurfuryl methacrylate and hydroxyalkyl methacrylates, di-, tri- or even higher polymethacrylates are employed. Such polyfunctional monomers may be used in blends with monofunctionals serving as cross-linking agents, or in compositions where monofunctional monomers are absent. In applications requiring high mechanical strength and chemical and wear resistance, in addition to low polymerization shrinkage and low exotherm of the curing process, higher molecular weight dimethacrylates are generally the monomers of choice. Such monomers are particularly useful in formulating modern self- and light-cured dental restorative materials, prostheses, cements, cavity liners, varnishes and sealers. Their use is also expanding in orthopedic surgery, where they are replacing, or being used as adjuncts to, monomethacrylate monomers to enhance mechanical properties and chemical resistance of resulting polymers.
Acrylic resins have unique features making them difficult to replace with other types of monomers, especially in particular or very demanding applications. These include ease of control of working and curing times, good biocompatibility, and a broad selection of available monomers, and relative ease of synthesizing new ones, having desirable molecular structures allows for modifying or controlling relevant characteristics of cured polymers such as water absorption, solubility, hydrophobicity, adhesive properties, compatibility with various additives, optical properties, mechanical strength, chemical resistance and resistance to heat and UV light. These properties allow for multiple ways of inducing polymerization, such as by chemical means, heat, or light.
These advantages make acrylic resin unique, important and often irreplaceable in many applications, especially in a dental field that has been revolutionized by their advent and consequent expansion.